The family Flaviviridae and genus Flavivirus encompasses a number of viruses that are potentially lethal human pathogens. Such viruses include Dengue virus, Yellow Fever virus, Modoc virus, and viruses of the Japanese encephalitis virus serogroup. The Japanese encephalitis virus serogroup includes several closely related viruses, such as Japanese encephalitis virus (JEV), West Nile virus (WNV), St. Louis encephalitis virus, Murray Valley encephalitis virus, and Kunjin virus. Kunjin virus is often referred to as a variant of WNV because of the degree of sequence conservation between these two viruses. Characterized WNV strains have been divided into two groups, lineage I and lineage II, based on sequence analysis.
In 1999, the first case of human WNV infection in the U.S. was reported. Since then, annual epidemics have occurred. In August 2002, transmission of WNV via routes other than mosquito bites was confirmed when four organ recipients were infected by a single organ donor. The virus has since been found to be transmissible by transfusion of blood products (21 confirmed cases) and by breast milk.
Detection of active WNV infection is difficult, as symptoms are non-specific and virus-specific antibodies can usually be detected only after the viremic phase. Furthermore, WNV-specific IgM can persist for more than a year, making it difficult to differentiate between active infection and past exposure. More sensitive detection methods, such as direct detection of viral nucleic acids, are needed. Detection of viral nucleic acids presents a more sensitive method for the early detection of infection by WNV and other flaviviruses than serological methods currently in use.
Other flaviviruses, including members of the Japanese encephalitis virus serogroup, are also human pathogens. These pathogens include Japanese encephalitis serogroup members such as Japanese encephalitis virus, St. Louis encephalitis virus (SLEV), and Murray Valley encephalitis virus, and other flaviviruses such as Dengue virus, Yellow Fever virus, and Modoc virus. Transmission of members of the Japanese encephalitis virus serogroup other than WNV via blood products remains undocumented. However, such transmissions are possible, and increasingly likely to occur as these viruses become more widespread. Therefore, new, sensitive, and specific assays that are capable of detecting these flaviviruses that are human pathogens are highly desirable. Furthermore, a single assay that is capable of detecting several members of the Japanese encephalitis serogroup would also be very desirable.